The grave digger is an unknown position, possibly within the Galactic Federation itself, that is involved in the career of grave keeping. These grave diggers, while only appearing in Dig, the Metroid Prime Hunters commercial, excavate graves for the recently deceased. They appear to be wearing sealed suits with gas masks, possible used for protection from pathological diseases and/or hazardous environments. They are seen using modified shovels with built in light sources.
Seeing as they only appear in the Metroid Prime Hunters commercial, their canonicity is ambiguous, though seeing as no sources contradict their existence and the fact that their "position" would be necessary, they may be part of Metroid continuity.